Optical systems incorporating waveguides and methods of manufacture

ABSTRACT

Methods for forming optical systems are provided. A representative method includes the steps of: providing a substrate; depositing on the substrate a first contoured channel preform of material capable of ion exchange with the substrate; and diffusing ions from the first channel preform into the substrate to form a first waveguide channel at least partially buried in the substrate. Optical systems and other methods also are provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application, which is based on andclaims priority to U. S. patent application Ser. No. 09/912,832 filed onJul. 24, 2001, now U.S. Pat. No. 6,751,391 and which is incorporatedherein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to optics. More specifically,the invention relates to systems and methods pertaining to opticalwaveguides.

2. Description of the Related Art

Optical communication systems are configured to propagate signalsbetween various locations. Through at least a portion of such acommunication system, the signals are provided as light that ispropagated along an optical path. Numerous optical communication systemsrely exclusively upon the transmission of single or lowest order modelight. For example, long distance and metro-range optical communicationsystems use single mode fiber. Single mode fiber offers a largerbandwidth than multi-mode fiber. This enables single mode fiber topropagate signals over greater distances than achievable with multi-modefiber without the use of repeaters, for example.

Optical signals of a communication system using single mode fiber areoften processed by various integrated optic devices. These integratedoptic devices can include modulators, interferometers, distributedfeedback elements, etc., all of which typically are based on planarwaveguide technology.

At various locations along an optical path of a communication system, itmay be desirable to reshape or scale the mode of light propagating alongthe optical path. For instance, mode typically is reshaped to satisfymode-match requirements of optical components positioned along anoptical path. For example, mode may be reshaped to accommodate atransition from an optical fiber to an integrated optic component. Asused herein, the term “mode” refers to the spatial distribution of lightrelative to a cross-sectional area oriented normal to the optical path.

Transformation of modal properties through axial tapering of adielectric waveguide is useful in several contexts. For example,mode-size transformation permits independent optimization of the modesize in different portions of the waveguide for effective input andoutput coupling. Mode-size transformation also can be used to obtain anarrow far-field of the outcoupled modes. An adiabatic taper from asingle-mode to a multi-mode waveguide also permits robust coupling intothe fundamental mode of a multi-mode waveguide. This is important incertain types of nonlinear waveguide devices that involve interactionsbetween modes at widely separated wavelengths.

A prior art solution for mode matching uses an optical fiber and amicro-lens, e.g., a spherical lens or gradient index lens. The opticalfiber and micro-lens allow for collection of light from the outputcomponent, e.g., an output fiber. The optical fiber and micro-lens alsoprovide input coupling of light into the input component, e.g., an inputfiber. Typical disadvantages of using such a solution include designdifficulties in providing components that are configured to receive theinput mode and provide an appropriately reshaped output mode.

Tapered optical fibers also have been used to reshape mode. A taperedoptical fiber includes one or more tapered portions, i.e., portions thathave cross-sectional areas that vary along their respective lengths. Thetapered portions of these fibers typically are formed by controlledincremental heating. For instance, by heating a portion of a fiber, thefiber core tends to expand, thus resulting in a localized increase incross-sectional area of the fiber. Simultaneous heating and pulling ofthe fiber results in a reduction of cladding and core dimensions. Apotential disadvantage of using tapered optical fibers includesdecreased mechanical strength of the fiber.

Additionally, integrated optic waveguides with continuous tapers andsegmented tapers have been used for reshaping mode. As used herein, theterm “segmented taper” refers to a waveguide taper that is composed ofor divided into portions with different optical properties that aredefined by dielectric boundaries. These dielectric boundaries are formedbetween the waveguide portions and portions of the substrate material,as viewed along the axis of light propagation. The term “continuoustaper” refers to a waveguide taper in which light, upon its propagation,does not traverse dielectric boundaries between the waveguide portionsand portions of the substrate material. Thus, in a waveguide withcontinuous taper, the taper changes its optical properties in acontinuous and adiabatic fashion.

Waveguides with segmented tapers are capable of providingtwo-dimensional mode tapering. However, these waveguides typically arelossy due to the multiple dielectric boundaries formed between thesegmented waveguide portions. In addition, precise control ofsegmentation is technologically involved. Therefore, it can beappreciated that there is a need for systems and methods that addressthese and/or other shortcomings of the prior art.

SUMMARY OF THE INVENTION

Optical systems and methods of the present invention relate to opticalwaveguides. A representative optical system of the invention includes asubstantially planar substrate and an elongate, two-dimensionallytapered waveguide channel at least partially buried in the substrate.

A representative method for forming an optical system includes:providing a substrate; depositing on the substrate a contoured channelpreform of material capable of ion exchange with the substrate; anddiffusing ions from the channel preform into the substrate to form awaveguide channel at least partially buried in the substrate.

Other systems, methods, features, and advantages of the presentinvention will be or become apparent to one with skill in the art uponexamination of the following drawings and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings. The components in the drawings are not necessarily to scale,emphasis instead being placed upon clearly illustrating the principlesof the present invention. Moreover, in the drawings, like referencenumerals designate corresponding parts throughout the several views.

FIG. 1 is a schematic diagram of a representative embodiment of anoptical waveguide of the present invention.

FIG. 2 is a cross-sectional view of the embodiment of FIG. 1.

FIG. 3 is a flowchart depicting a representative method for forming theembodiment of FIG. 1.

FIG. 4 is a schematic, side view of a representative substrate andchannel preform used to form the embodiment of FIG. 1.

FIG. 5 is a schematic, plan view of the embodiment of FIG. 4.

FIG. 6 is a cross-sectional view of the embodiment of FIG. 5 taken alongsection line 6—6.

FIG. 7 is a cross-sectional view of the embodiment of FIG. 5 taken alongsection line 7—7.

FIG. 8 is a cross-sectional view of the embodiment of FIG. 5 taken alongsection line 8—8.

FIG. 9 is a flowchart depicting a representative method for forming theembodiment of FIG. 1.

FIG. 10 is a schematic diagram of a representative apparatus that can beused for forming the embodiment of FIG. 1.

FIG. 11 is a schematic diagram of an embodiment of the invention thatincorporates a locating contour.

FIG. 12 is a schematic diagram of the embodiment of FIG. 11, showingdetail of a representative optical component aligned with the opticalpath of the waveguide channel.

FIG. 13 is a schematic diagram of an embodiment of the invention thatincorporates multiple waveguide channels.

FIG. 14 is a schematic diagram of a representative integrated opticalcomponent that can be formed from the embodiment of FIG. 13.

FIG. 15 is a schematic diagram of an embodiment of the invention thatincorporates multiple waveguide channels.

FIG. 16 is a schematic diagram of an embodiment of the invention thatincorporates multiple waveguide channels.

DETAILED DESCRIPTION

Referring now to the figures, wherein like reference numerals indicatecorresponding components throughout the several views, FIG. 1schematically depicts a representative embodiment of an optical system10 that incorporates a waveguide component 100. Waveguide component 100includes a waveguide channel 102 that is buried, at least partially, ina substrate 104, i.e., at least a portion of the waveguide channel doesnot intersect an exterior surface of the substrate. More specifically,waveguide channel 102 is defined by a presence of ions in a region ofthe substrate. The ions that define the waveguide channel are provided,at least in part, by a channel preform that includes material capable ofexchanging ions with the substrate. As described in greater detailbelow, the channel preform is applied to a surface of the substrateprior to waveguide channel formation.

Waveguide component 100 of FIG. 1 is shown in greater detail in thecross-sectional view of FIG. 2. In FIG. 2, waveguide channel 102 clearlyexhibits a change in cross-sectional area along at least a portion ofits length. In particular, a tapered portion 106 of the waveguidechannel exhibits a simultaneous taper in two dimensions. That is,tapered portion 106 exhibits a change in height (a change in dimensionrelative to the y axis) and a change in width (a change in dimensionrelative to the x axis). Unlike the embodiment of FIGS. 1 and 2, whichlacks continuous rotational symmetry about its optical axis, otherembodiments can exhibit continuous rotational symmetry. Additionally,although the height and width of the tapered portion depicted in FIGS. 1and 2 both change from narrow to broad in concert, other taperedportions can be formed where one of the height and width narrows as theother broadens.

Waveguide channel 102 also exhibits a continuous taper. Morespecifically, waveguide channel 102 lacks one or more interfaces betweenthe material of substrate 104 and the material of waveguide channel 102along the optical path. Also, waveguide channel 102 is a buriedwaveguide, i.e., no intermediate portion of the waveguide channelintersects an exterior surface 108 of the substrate.

The buried, two-dimensional, continuous taper of waveguide channel 102of FIGS. 1 and 2 potentially offers one or more advantages over knownwaveguide designs. For instance, compared to segmented-taper waveguides,waveguide component 100 tends to reduce or prevent unwanted reflectionsalong the optical path. This is because the continuously taperedconfiguration lacks interfaces between the material of substrate 104 andthe material of waveguide channel 102 along the optical path.Additionally, compared to non-buried waveguides, waveguide component 100potentially provides lower attenuation loss. More specifically, sincethe mode of waveguide component 100 is positioned away from the surface108 of substrate 104, the loss component of the waveguide attributableto scattering of the waveguide mode at the boundary defined by surface108 is reduced.

A representative method for forming waveguide component 100 will now bedescribed with reference to the flowchart of FIG. 3. In FIG. 3, method150 includes providing a substrate and applying a channel preform to thesubstrate (blocks 152 and 154). As described below, the substrate andchannel preform constitute a waveguide-forming structure. Ions from thechannel preform are then diffused into the substrate so that a waveguidechannel, which is at least partially buried in the substrate, is formed(block 156). A representative waveguide-forming structure that can beused to form the waveguide component 100 of FIGS. 1 and 2 is depicted inFIG. 4.

Waveguide-forming structure 200 of FIG. 4 includes a substrate 202 and achannel preform 204. In FIG. 4, substrate 204 is depicted as asubstantially planar substrate. It should be noted, however, thatvarious other shapes of substrates can be used. Channel preform 204,which approximates the shape of the ultimate waveguide channel, can beapplied to the substrate by various techniques. For instance, a materialdeposition process can be used.

As shown in FIGS. 4 and 5, channel preform 204 includes a first endportion 210 and a second end portion 212. The first and second endportions exhibit generally uniform cross-sectional areas, i.e., areas inthe x-y plane, along their respective lengths. An intermediate portion214 is arranged between the first and second end portions. Intermediateportion 214 is a generally wedge-shaped structure (as viewed in the sidecross-section of FIG. 3). More specifically, intermediate portion 214includes an upper surface 216 that is inclined relative to an uppersurface 218 of substrate 202. The inclined upper surface of intermediateportion 214 generally corresponds to the taper in the y dimension oftapered portion 106 of waveguide channel 102 (FIGS. 1 and 2).

Intermediate portion 214 also is defined by sidewalls 220 and 222. Asviewed along the z axis from first end portion 210 to second end portion212, sidewalls 220 and 222 angle outwardly from each other. Thesidewalls 220 and 222 of intermediate portion 214 generally correspondto the taper in the x dimension of tapered portion 106 of waveguidechannel 102 (FIGS. 1 and 2).

Cross-sections of waveguide-forming structure 200 are depicted in FIGS.6–8. As shown in FIGS. 6–8, channel preform 204 is partially defined byinclined sidewalls 224 and 226. Inclined sidewalls 224 and 226 extendupwardly from sidewalls 220 and 222, respectively, and terminate atupper surface 216. Thus, the inclined sidewalls extend inwardly from thesidewalls to form beveled portions 228 and 230 of the channel preform.Improved circularity of the mode propagated through a waveguide formedfrom waveguide-forming structure 200, for example, can be attributed, atleast in part, to this beveled configuration.

It should be noted that the shapes of actual channel preforms used toform waveguide channel similar to those depicted in FIGS. 1 and 2 mayonly approximate the shapes depicted in FIGS. 4 through 8. For instance,due to material and/or manufacturing limitations, channel preform 204may be formed by multiple, sequentially applied, deposition layers ofmaterial. Thus, sidewalls of the actual channel preform may exhibitstepped exterior surfaces in contrast to the smooth exterior surfacesdepicted. In order to obtain a channel preform with smoother exteriorsurfaces, which may be preferred in some applications, a depositiontechnique known in the art as “shadow masking” can be used.

Embodiments of waveguides can be formed with channel preforms that areshaped differently than those depicted in FIGS. 4–8. By way of example,channel preforms can exhibit cross-sectional areas of various shapes,such as rectangular. Additionally, channel preforms may vary inthickness along at least a portion of their respective lengths in eitheror both of width (x) and height (y). In some embodiments, a channelpreform can be formed of multiple preform segments. For instance, such achannel preform could include multiple preform segments that arearranged in tandem and/or in a side-by-side relationship for forming asingle waveguide channel.

By using one or more channel preforms to form a waveguide channel 102,various types of waveguides can be provided. For example, tapering of awaveguide channel 102 may be continuous or segmented. Additionally,tapering may occur in one dimension or in two dimensions, e.g.,simultaneously or independently tapering in height and width. Regardlessof the particular shape of the waveguide channel, the waveguide channelexhibits a refractive index that is higher than that the correspondingsubstrate. Therefore, light entering the waveguide channel tends topropagate along an optical path defined by the waveguide channel.

Another representative method for forming a waveguide component, e.g.,waveguide component 100 of FIG. 1, will now be described with referenceto the flowchart of FIG. 9. As depicted in FIG. 9, method 250 includesproviding a substrate and depositing a channel preform on the substrate(blocks 252 and 254). This yields a waveguide-forming structure, e.g.,waveguide forming structure 200 of FIG. 3. In block 256, an ionic liquidis provided. The waveguide-forming structure is immersed in the ionicliquid (block 258) so that a first portion of the liquid engages thechannel preform and a second portion of the liquid engages thesubstrate. An electric potential then is applied across the firstportion and the second portion of the ionic liquid (block 260) so thations from the channel preform diffuse into the substrate to form awaveguide channel.

Substrates used to form waveguide components of the invention, such asby the representative method depicted in FIG. 9, can be formed ofvarious materials. By way of example, various glass compositions may beused. More specifically, substrates can be formed of chalcogenideglasses, halide glasses, phosphate glasses, boroalumino-silicateglasses, and tellurite glasses, among others. Additionally, embodimentsmay utilize glasses doped with active rare-earth ions, such as Er³⁺,Tm³⁺, and Nd³⁺, for example. Active ions can be used to obtain opticalsignal amplification in different spectral regions, e.g., active ionsare used in fabrication of fiber or waveguide amplifiers.

Other materials used in integrated optics can be used as substratesdepending on the requirements of a particular application. For instance,a substrate material may be chosen for particular material properties,such as optical loss, active characteristics, mechanical stability,compatibility with high-volume batch processing techniques, and cost,among others. A substrate material also may be chosen for particularapplication suitability, such as intended spectral range of operation.Additional examples of potentially suitable substrates includesemiconductor crystals, e.g., A^(II) B^(IV), A^(III) B^(V), dielectriccrystals, such as Lithium Niobate and KTP, and organic compounds.

Waveguide channels, such as waveguide channel 102 of FIGS. 1 and 2, alsocan be formed from various materials. More specifically, variousmaterials that are capable of exchanging ions with the material of thesubstrate can be used to form a waveguide channel. The ions used to formsuch a waveguide channel can be provided from a channel preform and/oran ionic liquid. By way of example, monovalent cations, such as Silver(Ag⁺), Lithium (Li⁺), Potassium (K⁺), Rubidium (Rb⁺), Cesium (Cs⁺), andThallium (Tl⁺) can be used to exchange ions with the substrate. Forinstance, when the substrate comprises glass containing Na₂O, Na⁺present in the glass can be exchanged with the monovalent cations. Morespecifically, Na⁺ present in the glass can be exchanged with Ag⁺ from achannel preform containing Silver and Na⁺ from an ionic liquid of SodiumNitrate. Furthermore, in the presence of an electric field(s),waveguides can be obtained by diffusion of monovalent as well asbivalent cations, such as Zinc (Zn²⁺). By way of another example, theexchange between three ions can proceed simultaneously when a substratecontains one type of alkali cations and the ion source involves alkalications of two types, and vice versa. The selection of substrate,channel preform and/or ionic liquid materials can be based on knownmaterial properties and the requirements of a particular application aswould be known to one of ordinary skill in the art.

FIG. 10 schematically depicts a representative apparatus 300 that can beused to implement the method of FIG. 9. In FIG. 10, ionic liquid 302 isprovided in a container 304 of apparatus 300. In some embodiments, theionic liquid can include a salt, such as Sodium Nitrate (NaNO₃), that ismaintained in a molten state. Preferably, the material(s) forming theionic liquid are maintained at or above a temperature that is requiredto maintain the material(s) in liquid form. For example, Sodium Nitrate(NaNO₃) should be maintained at or above approximately 307° C.

Apparatus 300 also includes a support structure 306 that is adapted tosuspend waveguide-forming structure 200 within the ionic liquid. In theembodiment of FIG. 10, support structure 306 defines an opening 308.Opening 308 permits a first portion 310 of the ionic liquid to contactsubstrate 202 and a second portion 312 of the ionic liquid to contactchannel preform 204.

An electric potential is applied across the waveguide-formingstructure200 via the ionic liquid. This causes ions of the channelpreform to indiffuse to the substrate. Burial of the ions that form thechannel preform begins when ions of the ionic liquid, e.g., Na⁺, startto re-build the matrix of the substrate above the channel preform. Thisprocess is referred to as “one-step field-assisted ion-exchange usingthe solid source of ions and molten-salt electrodes.” For convenience,the term “one-step field-assisted ion-exchange fabrication” is usedherein.

One-step field-assisted ion-exchange fabrication is considered animprovement over the teachings of Pantchev. See, Multimode StripWaveguide Formed by Ion-Electro-Diffusion from Solid State Silver: SideDiffusion Reduction, B. Pantchev, Optics Communications, v.60, p. 373,1986, which is incorporated by reference herein. Compared to Pantchev'sfabrication technique, the one-step field-assisted ion-exchangefabrication technique simplifies waveguide fabrication. Morespecifically, the only deposition steps required are those associatedwith applying the channel preform 204 to the substrate 202. Moreover,the waveguide is formed and, at least partially, buried during a singleprocess step.

Perceived enhancements over Pantchev may be attributed to variouscauses. For instance, the one-step field-assisted ion-exchangefabrication technique enables application of a substantially uniformelectric field over the entire substrate. Additionally, the large heatmass associated with the molten salt reduces the potential of thewaveguide-forming structure from being subjected to substantialtemperature variations during processing. The one-step field-assistedion-exchange fabrication technique also tends to reduce side-diffusionof ions of the channel preform. Thus, lateral broadening of thematerial, e.g., broadening in the x-y plane, during indiffusion isreduced. As a result, more circular modes have been demonstrated. Thischaracteristic should enhance waveguide to fiber coupling.

A representative example of a waveguide component 100 that can be formedby the one-step field-assisted ion-exchange fabrication technique isdepicted in FIG. 11. Waveguide component 100 incorporates a waveguidechannel 102 that includes a first end 350 and a second end 352. Thefirst end and second end can function as input and output, respectively,or vice versa. In the embodiment of FIG. 11, the first and second endsare generally planar in shape and are oriented substantially orthogonalto the optical path of the waveguide channel. In other embodiments, theends can take on various other shapes and/or orientations.

Waveguide component 100 of FIG. 11 also includes a locating contour 354.The locating contour facilitates alignment of an optical component(s)with the optical path of the waveguide channel. For instance, FIG. 12depicts a representative optical component 356 that is aligned with theoptical path of waveguide channel 102. Alignment can be achieved byengaging a surface, e.g., surface 358, of optical component 356 with thelocating contour 354. In this embodiment, further alignment is achievedby engaging an additional surface, i.e., surface 360, of the opticalcomponent with the second end 352 of the waveguide channel.

Another representative embodiment of a waveguide component 100 isdepicted in FIG. 13. In FIG. 13, waveguide component 100 incorporates awaveguide channel 102 that includes multiple tapered channel portions.In particular, waveguide channel 102 includes tapered channel portions370A, 370B that are arranged in tandem. A linking portion 372 is locatedbetween the tapered channel portions. Linking portion is defined by aregion of ions present in the substrate that interconnects the taperedchannel portions. In some embodiments, the tapered channel portions andthe linking portion can be formed from a single contoured channelpreform.

In the embodiment of FIG. 13, linking portion 372 is a non-taperedportion of the waveguide channel that is sized and shaped to accommodatethe formation of a trench. As described later, the trench should besized to receive one or more optical components. Material to be removedfrom linking portion 372 to form such a trench may be removed by etchingor any other suitable removal process.

In FIG. 13, each tapered channel portion is configured to propagatecollimated light from its second end, i.e., ends 374A, 374B. Typically,linking portion 372 is defined within the partially overlapping Rayleighranges of the tapered portions so that removal of at least a portion ofthe linking portion does not disrupt propagation of collimated lightbetween the tapered portions. Preferably, the length of the linkingportion is established to accommodate the manufacturing toleranceassociated with forming the trench so that collimated outputs of thetapered portions are not disturbed after trench formation. In thismanner, a trench can be formed at various locations along the length ofthe linking portion.

In FIG. 14, a portion of the linking portion 372 and surroundingsubstrate has been removed to form a trench 380. Trench 380 is partiallydefined by locating contour 382. As shown in FIG. 14, trench 380 issized to receive one or more optical components. In particular, trench380 is depicted as at least partially receiving an optical component384. Optical component 384 can include one or more of various elementsincluding rotators, beamsplitters, re-routers, isolators, reflectors,refracting elements, diffracting elements, filters, and circulators.Thus, waveguide component 100 and optical component 384 can function asan integrated optical beamsplitter (polarizing or non-polarizing),isolator, distributed Bragg reflector, circulator, rotator, or filter(polarizing or non-polarizing), for example.

Another representative embodiment of a waveguide component 100 isdepicted in FIG. 15. Waveguide component 100 of FIG. 15 incorporates awaveguide channel 102 that includes multiple tapered channel portions370A, 370B, 370C. In some embodiments, the channel portions 370A, 370B,370C can be formed from a single channel preform. Each of the taperedchannel portions optically communicates with a trench 380. Trench 380 isadapted to receive, at least partially, an optical component 384. Forinstance, optical component 384 can be a polarizing beamsplitter. Insuch an embodiment, light of an arbitrary polarization (depicted byarrow 386) can be propagated to the polarizing beamsplitter via channelportion 370A. The beamsplitter directs light of a first polarization toone of the remaining waveguide channels, e.g., channel portion 370B.Light of the first polarization is then propagated from channel portion370B (depicted by arrow 388). Light of a second polarization, which isorthogonal to the first polarization, is directed to the other channelportion, e.g., channel portion 370C. Light of the second polarization isthen propagated from channel portion 370C (depicted by arrow 390). Inthis manner, the waveguide component of FIG. 15 can function as apolarizing integrated optic re-router.

The embodiment of FIG. 15 can be adapted to receive a single light inputand, in response to the input, provide either a single output ormultiple, e.g., simultaneous, outputs. Alternatively, the waveguidecomponent can be adapted to receive multiple inputs and, in response tothe inputs, provide a single output.

The one-step field-assisted ion-exchange fabrication technique of theinvention also can be used to form an array of waveguides. Morespecifically, multiple waveguide channels can be formed on a singlesubstrate. This is accomplished by applying multiple channel preforms tothe substrate and indiffusing ions of the channel preforms to thesubstrate to form the waveguide channels. Thus, embodiments of theinvention are considered batch-processing and array-configurationcompatible. This can significantly reduce the cost of waveguide devicefabrication, for example.

A representative embodiment of a waveguide array 400 that includesmultiple waveguide channels is depicted in FIG. 16. In FIG. 16, array400 includes waveguide channels 102A, 102B, 102C, 102D, 102E and 102Fformed on a substrate 104. The waveguide channels are arranged in pairs,with the waveguide channels of each pair being arranged in tandem. Inother embodiments, other numbers of waveguide channels can be provided.

Each of the waveguide channels communicates with a transmission medium,such as an optical fiber or other optical component. More specifically,waveguide channel 102A communicates with transmission medium 402A,waveguide channel 102B communicates with transmission medium 402B,waveguide channel 102C communicates with transmission medium 402C,waveguide channel 102D communicates with transmission medium 402D,waveguide channel 102E communicates with transmission medium 402E, andwaveguide channel 102F communicates with transmission medium 402F.

A trench 380 is located between the waveguide channels of each tandempair. Trench 380 is defined, at least in part, by locating contour 354.Trench 380 is sized to receive one or more optical components and, inthe embodiment of FIG. 16, spans between the multiple tandem pairs ofwaveguide channels. In other embodiments, a separate trench can beformed between each or a subset of the tandem pairs of waveguidechannels.

In FIG. 16, trench 380 at least partially receives optical components384A, 384B and 384C. Each of the optical components opticallycommunicate with a respective tandem pair of waveguide channels. Thus,an optical signal (depicted by arrow 404) can be propagated to waveguidechannel 102A via transmission medium 402A, through optical components384A and 384B, and then to transmission medium 402B (depicted by arrow406), or vice versa.

The foregoing description has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Modifications orvariations are possible in light of the above teachings. The embodimentor embodiments discussed, however, were chosen and described to providethe best illustration of the principles of the invention and itspractical application to thereby enable one of ordinary skill in the artto utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated.

By way of example, field-assisted ion-exchange methods other than theone-step field-assisted ion-exchange fabrication technique disclosedhere are known in the art. These other field-assisted ion-exchangemethods can be used to form various optical systems disclosed and/orclaimed herein. Additionally, the representative embodiments depictedherein are shown with inputs at the ends of the waveguide channelsexhibiting the smaller cross-sectional areas. However, either end of awaveguide channel may be used as an input as determined by themode-matching requirements of a particular application. Moreover, insome embodiments, a waveguide channel may not include a tapered portion.All such modifications and variations, are within the scope of theinvention as determined by the appended claims when interpreted inaccordance with the breadth to which they are fairly and legallyentitled.

1. An optical system comprising: a substrate; a channel preformcomprising a material operable to provide electrolytic ion exchange withsaid substrate, said channel preform exhibiting a change incross-sectional area along at least a portion of a length of saidchannel preform; and a waveguide channel comprising ions that arediffused by electrolysis from said channel preform into said substrate,wherein at least a portion of said waveguide channel is at leastpartially buried in said substrate, said waveguide channel exhibiting achange in cross-sectional area along at least a portion of a length ofsaid waveguide channel substantially the same as the change incross-sectional area of said channel preform.
 2. The optical system ofclaim 1, wherein the change in cross-sectional area comprises acontinuous taper from a first cross-sectional area to a secondcross-sectional area.
 3. The optical system of claim 2, wherein thefirst cross-sectional area is larger than the second cross-sectionalarea.
 4. The optical system of claim 2, wherein the first and secondcross-sectional areas are circular cross-sectional areas.
 5. The opticalsystem of claim 2, wherein the first and second cross-sectional areasare non-circular cross-sectional areas.
 6. The optical system of claim1, wherein said waveguide channel is completely buried in saidsubstrate.
 7. The optical system of claim 1, wherein said channelpreform comprises at least one of a silver cation, a lithium cation, apotasium cation, a rubidium cation, a cesium cation, and a thalliumcation.
 8. The optical system of claim 1, wherein said substrate is asubstantially planar substrate.
 9. The optical system of claim 1,wherein the change in cross-sectional area of said channel preformcomprises a step change from a first cross-sectional area to a secondcross-sectional area.
 10. The optical system of claim 1, wherein saidwaveguide channel comprises a material operable to provide electrolyticion exchange with an ionic liquid.
 11. The optical system of claim 1,wherein said substrate comprises at least one of a chalcogenide glass, ahalide glass, a phosphate glass, a boroalumino-silicate glass, atellurite glass, a glass doped with rare-earth ions, a semiconductorcrystal, and a dielectric crystal.